The present invention relates to a device for providing electrical connection between a current output terminal and an electrochemical stack in a storage battery, and an associated manufacturing method.
An electrochemical cell or storage battery (these two terms being equivalent, the term storage battery will be used hereinafter) is a device for producing electricity in which chemical energy is converted into electrical energy. The chemical energy is constituted by electrochemically active compounds deposited on at least one face of electrodes arranged in the storage battery. The electrical energy is produced by electrochemical reactions during discharge of the storage battery. The electrodes, arranged in a container, are electrically connected to current output terminals to provide electrical continuity between the electrodes and an electrical consumer with which the storage battery is associated. The positive and negative current output terminals can be secured either onto the walls of opposing sides of the container of the storage battery, or onto the wall of a same side of the container.
FIG. 1 shows a sealed cylindrical storage battery of a known type.
Storage battery 1 comprises an electrochemical stack 9 comprising alternating positive and negative electrodes on either side of separators impregnated with electrolyte. Typically, each electrode is made up by a metal current collector also called a foil, carrying on at least one face thereof, the electrochemically active matter. The electrochemical stack 9 is arranged in a sealed container 2 having a cylindrical wall closed off by a base 3 at one end thereof and covered at the other end by a lid 5 which carries the current output terminals 6 and 7. A first current output terminal, in the example the positive terminals 6, is generally welded onto the lid. A second current output terminal, in the example the negative terminal 7, passes through the lid; it is generally secured onto the latter by crimping, with seals 8 electrically insulating the negative current output terminal 7 from the lid 5.
The current output terminals 6, 7 provide electrical continuity between the electrodes and the external application with which the storage battery is associated. There exist several ways of electrically connecting the electrodes of a given polarity to one of the current output terminals on the container. One possible solution consists in employing a flat connection applied onto the collectors of the electrodes having the same polarity. This known solution is illustrated on FIG. 1; a flat connection 11 connects the positive electrodes of electrochemical stack 9 together, and a conducting shaped part 12 connects this flat connection 11 to the bottom wall 3 of the container, the walls of the container being electrically conducting with the lid 5 and the positive terminal 6 welded onto the lid. Similarly, a flat connection 13 connects the negative electrodes of electrochemical stack 9 together, and an elongated tab 14 connects this flat connection 13 to the negative current output terminal 7. The elongated tab 14 forms at least one bend in order to impart an elastic effect to the electrical connection between the negative electrodes and the negative current output terminal, and which compensates for variation in height of electrochemical stacks from one storage battery to another.
Typically, the device for providing electrical connection to the terminal passing through the container wall—in the example of FIG. 1 this is the negative terminal—is assembled in the following way. Flat connection 13 is welded onto the collectors of the electrodes of a given polarity after which the elongated tab 14 is welded onto the flat connection 13 and onto the lower portion of through terminal 7. The elongated tab 14 is then bent inside the storage battery while the container 2 is being closed by the lid 5. The operation of bending and positioning the elongated tab inside the storage battery is generally done manually and is complicated.
EP-A-0,029,925 discloses an electrical connection device comprising a full disc which is arranged and welded onto the edge portions of the roll of spirally-wound electrodes. This full disc is provided with an elongated tab which is welded to a sealing disk in contact with one of the current output terminals.
U.S. Pat. No. 4,009,053 discloses an electrical connection device comprising a flat circular connection incorporating radial slots in the form of slashes, the bent over edges of which act to provide electrical contact with the collectors of the spirally-wound electrodes.
EP-A-1,102,337 discloses a storage battery comprising a spirally-wound electrochemical stack. Each electrode has a metal foil acting as the current collector. The foils of a given polarity respectively project externally of the electrochemical stack and are bent over to form a flat base onto which an elongated flat connection tab is welded.
French patent application 2,748,006 discloses a method of connection by bundling. Edge portions of the electrodes are brought together into two half-bundles connected horizontally to a current output terminal.
EP-A-1,596,449 discloses a connection device comprising a flat connection welded onto a substantially flat base plate formed by the folded foils of the electrodes of a given polarity. An elongated folded tongue is then welded between the flat connection and the bottom portion of the current output terminal passing through the container wall.
U.S. Pat. No. 3,761,314 discloses a connection device comprising a flat connection welded onto the folded foils of the electrodes of a given polarity. The flat connection is in direct contact with the current output terminal, elasticity of the connection being insured by the folding of the foils of the electrodes.
EP-A-0,955,682 discloses a connection device comprising electrical connection strips welded onto the folded ends of the foils of the electrodes of a given polarity.
There exists a need for a simplified electrical connection device; in particular, for a device providing connection between the same-polarity electrodes and a current output terminal passing through a wall of the container which dispenses with the elongated connection tab, and which requires no welding to the current output terminal.